1. Field of the Invention
The present invention relates to a solid-state imaging apparatus with pixels arranged along rows and columns, each pixel including a photoelectric conversion element.
2. Description of the Related Art
It has been known that an MOS amplifying type solid-state imaging apparatus such as a CMOS sensor performs a global electronic shutter operation. In a global electronic shutter operation, all the pixels arranged along rows and columns simultaneously start and finish their respective photoelectric charge accumulation.
For a global electronic shutter operation, it is necessary to provide a charge accumulating unit that accumulates charges generated as a result of photoelectric conversion for a predetermined period of time in each pixel.
In general, a common signal line is provided for each pixel column, and thus, the charge accumulating unit assumes the role of accumulating changes from the end of pixel accumulation until the start of reading for a certain relevant pixel. Accordingly, if light enters the charge accumulating units while charges are being accumulated in the charge accumulating units, resulting in generation of charges by means of photoelectric conversion, such charges become noise, which may deteriorate the image quality.
In order to solve the problem, National Publication of International Patent Application No. 2006-523034 describes a light shield having a light shielding function being provided in each pixel. These light shields are fixed to a common ground potential. Each light shield includes an aperture for introducing light to a photo diode and an aperture for connecting an electrode arranged below the light shielding and a wiring.
Also, Japanese Patent Application Laid-Open No. 2007-157912 employs the technique of providing a space around each charge accumulating unit, and connecting the gaps and a light shielding layer provided above the charge accumulating units, thereby protecting the accumulation units by means of the total reflection by the gaps and the light shielding layer.
A CMOS sensor requires the drive control of transistors in each pixel, and thus, requires an electric connection structure, such as a plug, from the wiring layer to the substrate via a light shielding portion. In such a technique as disclosed in National Publication of International Patent Application No. 2006-523034, which is based on the notion that all the components of each pixel, other than a photo diode, are covered, and thus, a light shielding film is provided with an aperture in a position in which the substrate and the wiring layer are electrically connected.
However, when an aperture is provided in a light shielding portion, light may leak under the light shielding portion as a result of, e.g., the light directly passing through the aperture or propagating while being diffracted. For obtainment of an effect equivalent to light shielding by means of a physical mechanical shutter, the strict characteristic of a light shielding effect of no less than one hundred thousand to one, that is, only one part of light leaks into a charge accumulating unit per one hundred thousand parts of light entering the pixel may be required. However, where a light shielding portion is provided with an aperture, such effect cannot be expected.
Also, in Japanese Patent Application Laid-Open No. 2007-157912, all the incoming light is not always subject to total reflection, and light not satisfying the conditions for a critical angle may not be blocked, resulting in entering the charge accumulating units.
Furthermore, National Publication of International Patent Application No. 2006-523034 and Japanese Patent Application Laid-Open No. 2007-157912 both contemplate only the case where the accumulation units are simultaneously driven for the entire imaging area. Thus, they do not deal with an operation particular to CMOS sensors, called “line exposure operation”.
The present invention has been made in view of the above problems, and aims to provide a configuration enabling a line exposure operation while preventing lowering of the light shielding effect for the charge accumulating units.